The two lunar missions, which together cost some &dollar;580 million, are NASA’s first since 1998 and are intended to pave the way for a potential human settlement on the moon. “We will prepare … the guidebook for future exploration of the moon,” LRO project scientist Richard Vondrak told reporters on Tuesday.

LRO will arrive at the moon after about four days and is expected to spend several years in orbit, mapping the lunar surface using a suite of instruments including cameras and an advanced laser altimeter. The altimeter will fire five laser beams 28 times per second to build up 3D maps of the surface.

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Landing sites

The orbiter’s first year will focus on NASA’s human exploration goals, mapping the moon in unprecedented detail, while honing in on 50 ‘high-priority’ locations that have been identified as prime landing sites for future manned missions. The mission may then be extended for three years to conduct scientific observations.

Meanwhile, the short-lived LCROSS mission has just one target. After several months in Earth orbit, in early October the spacecraft will shepherd the 2400-kilogram upper stage of the launch rocket into a collision course with the moon’s south pole.

NASA believes the moon’s poles are the best places for a potential lunar outpost. That’s partly because some portions of the poles are almost continuously lit, which could be a boon for solar power collection.

Double impact

But the regions could also be rich in water needed for long stays on the lunar surface. In 1998, NASA’s last moon probe, Lunar Prospector, found that large areas of the poles seemed to contain hydrogen. That hinted that water deposited by ancient impacts could be preserved in some craters whose high rims keep their interiors permanently shaded from the sun (though other lines of evidence have yielded contradictoryfindings on the question of ice).

The LCROSS mission will excavate some of this long-hidden material so it can be illuminated by sunlight and observed by ground and space telescopes, including Hubble, LRO, and India’s lunar orbiter Chandrayaan-1.

LCROSS will follow behind the Centaur stage to take its own measurements of the impact before crashing into the moon about four minutes later.

The Centaur impact is expected to excavate more than 350 tonnes of lunar material, creating a crater 20 metres wide and sending a plume of material several kilometres above the surface. The LCROSS probe itself will throw up an estimated 150 tonnes of material, gouging out a crater 14 metres wide.